In this latest round of legal action, ClientEarth has lodged papers at the High Court in London seeking judicial review and has served papers on government lawyers.

As well as the UK Environment Secretary who is named as the defendant, Scottish and Welsh ministers, the Mayor of London and the Department for Transport will also be served with papers as interested parties in the case.

The UK sees an estimated 40,000 early deaths from air pollution every year. ClientEarth believes the government is in breach of a Supreme Court order to clean up air quality, having failed once again to take appropriate action in the face of this public health crisis.

The plans the government came up with, released on 17 December last year, wouldn’t bring the UK within legal air pollution limits until 2025. The original, legally binding deadline passed in 2010. The papers lodged with the High Court ask judges to strike down those plans, order new ones and intervene to make sure the government acts.

ClientEarth lawyer Alan Andrews said: “The government’s plans were an insult to the tens of thousands of people being made sick and dying from air pollution and failed to consider strong measures to get the worst polluting diesel vehicles out of our town and city centres.

“As the government can’t be trusted to deal with toxic air pollution, we are asking the court to supervise it and make sure it is taking action.”

A YouGov poll for ClientEarth this week revealed air pollution is Londoners’ biggest health concern, topping a list which included smoking, stress and alcohol.

In the survey, of more than 1,000 London adults, three out of four said they backed legal action to force the government to deal with air pollution.

Alan Andrews added: “It is a disgrace that we have had to take further legal action to force the government to protect our health. It must act urgently to tackle this public health crisis.”

Utah, Colorado and Texas are being aggressively pumped for oil and natural gas, producing methane leaks in quantities much higher than previously thought – and little is being done to contain the problem.

When Stephen Conley, an atmospheric scientist and pilot, saw an emissions indicator skyrocket in his Mooney TLS prop plane, he knew he had found a significant methane leak. His gas-detecting Picarro analyzer indicated he was flying through a plume of gas escaping at 900kg per hour. The colorless, odorless gas was enough to cover a football field to a height of 20 feet [6 m] in a single day. But this flight wasn’t over the highly publicized Aliso Canyon in Los Angeles; Conley was circling the Bakken Shale, a rock formation in western North Dakota that has been aggressively pumped for oil and natural gas.

“There’s all these small leaks everywhere and they eclipse [Aliso Canyon],” said Paul Wennberg, professor of atmospheric chemistry and environmental science and engineering at the California Institute of Technology.

The results have been striking. Researchers from the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado Boulder found methane escaping from Utah’s oil and gas producing Uintah Basin at 55 metric tons per hour. The same researchers found oil and gas related methane in Colorado’s Denver-Julesburg Basin leaking at 19.5 metric tons per hour. In the Barnett Shale area of North Texas, methane emissions were sampled at 60 metric tons per hour.

Leaks found in Utah, Colorado and Texas, however, are believed to be ongoing and there are currently few efforts to contain them. (Colorado recently enacted new emissions laws, though their efficacy has yet to be determined.) There are many other areas where no testing has been done at all.

“Aliso Canyon maybe represents one half of what’s coming out of a small basin like the Denver-Julesburg area, but a much smaller fraction of something like the Uintah Basin or Barnett in Texas,” said Colm Sweeney, lead scientist for the NOAA Earth System Research Lab Aircraft Program.

Researchers at NOAA report finding methane – the primary component of natural gas – leaking from the entire natural gas supply chain, from extraction to storage to transmission. The leaks can come from improperly sealed fittings, faulty valves and compressors, improperly closed hatches and many other sources, stemming from both human error and equipment failure. “There’s no really compelling smoking gun that one particular type of thing leaks more than another,” said Dan Zimmerle, director of the Electrical Power Systems Laboratory at Colorado State University.

Zimmerle is co-author of several papers that have tested for onsite leaks at a number of major natural gas companies; none of the companies whose facilities were tested were found to be leak-free. These include Access Midstream (now a part of Williams Corporation), Anadarko Petroleum Corporation, Hess Corporation, Southwestern Energy and Williams Corporation. In an email from company spokesman Tom Droege, Williams Corporation said it was committed to finding environmentally responsible ways of developing natural gas, “including ensuring that methane emissions are addressed and lowered”. Droege pointed to the company’s voluntary participation in the study as proof of its commitment.

While government agencies have not consistently tested for methane leaks, plumes can often be traced relatively easily from the air. NOAA’s Sweeney likens atmospheric research flights to “mowing the lawn”, or taking a back and forth route across a predetermined area to avoid missing any patches. Dead grass along transmission lines often indicates a methane leak. And methane plumes within 20km of a flight path can easily be traced directly back to a specific facility or well, Sweeney said.

The difficulty in detecting leaks in rural areas remains great, however, simply because little to no regular monitoring takes place. Conley, who helped investigate the Aliso Canyon leak, said he believed that leak was discovered and quantified only because it began in a populated area. The leak occurred at a point in the distribution line at which an odor had been added to the gas that could be detected by local residents. Without the odor and without direction to fly over Aliso Canyon from the California Energy Commission, with whom Conley had a contract, the full extent of the Aliso Canyon leak might not have been detected for some time. “That to me is the scariest take-home from all of this. That this [detection] all happened because of luck,” Conley said.

Most scientists concede that a certain amount of methane loss is to be expected as part of natural gas production, but nearly all agree the current numbers are far too high. In fact, researchers have found methane losses of nearly 17% of production in the Los Angeles Basin, losses of 6-12% of natural gas production in the Uintah Basin and losses of approximately 4% of production in the Denver-Julesburg Basin.

“It shouldn’t be nearly as high as what we’re reporting, even in the underreported cases,” said David Babson, senior fuels engineer at the Union of Concerned Scientists. “It shouldn’t be as high as two or three or four percent higher. It should definitely be near zero.”

“It’s not hard to see how a lot of little problems over the course of a year add up to some fairly big numbers”, said Mark Brownstein, vice president of the EDF’s Climate and Energy Program. “Both in terms of total amount of methane being lost, but also the climate impact that that has.”

The EPA bases its current regional emissions estimates on typical equipment and processes used in oil and gas production. That is a big problem, according to the Union of Concerned Scientists. “Those systematic tests don’t pick up the day that the valve was stuck open, or the day that there’s a liquid unloading event that has a whole bunch of methane emissions and so you don’t capture the true amount of methane,” Babson said.

A 2013 study in the Proceedings of the National Academy of Sciences estimates that anthropogenic emissions of methane in the US could be off by as much as 50%. That in turn means that climate change modeling data produced by the EPA could be seriously flawed.

In many cases, fixing a methane leak is as simple as tightening a valve or closing a hatch; the trick is simply knowing which valve or hatch requires such attention. Colorado State’s Zimmerle likened the process to a game of “Whac-A-Mole.” “This type of failure is almost impossible to prevent entirely and so good detection methods followed by good repair practices would be an effective way to control this,” he said.

To date, the government has made painfully slow progress toward addressing methane emissions. In 2014, the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) announced $30m in funding for programs to address methane emissions from energy production. And the White House announced in January 2015 a plan to cut US methane emissions from 2012 levels by 2025. Though if the 2012 emissions estimates are inaccurate, that plan likely requires revisiting.

The EPA is also currently developing rule changes to address methane emissions in new and modified oil and gas projects. But the agency has yet to address methane leaks at existing facilities.

Gas producers stand to benefit from repairing leaks because they are able to sell what doesn’t escape. “If you make the fix, then you’re seeing added gas sales or added gas volumes, compared to if you didn’t make the fix, although there is an upfront cost,” said Nicholas Potter, a natural gas analyst at Barclays. “There is a potential savings there if leaks can be prevented.”

In an August 2015 report, Barclays described the current technologies being used to limit methane emissions under normal economic conditions as having “relatively reasonable upfront costs and depending on natural gas price levels pay back periods below three years”. Potter said when gas prices drop, however, that leads to less financial incentive to act.

But before the leaks are fixed, they need to be detected. For Conley and others, that can only be achieved through regular, independent monitoring. “It would be great to go back to all of the major fields and do it every month,” Conley said.